The W3C Timed Text Markup Language (TTML) [TTML2] is an XML vocabulary for video subtitles and captions.

Like many other XML vocabularies, TTML works as a baseline and covers many known use cases. One use case is the exchange of subtitle files, another use case is the rendering of subtitles in a video player. That's why it comes to no surprise that in operation not the complete TTML vocabulary is used, but only subsets of the Markup Language.

Examples of these subsets are EBU-TT-D [EBUTTD] defined by the European Broadcast Union (EBU) and the widely adopted TTML Profiles for Internet Media Subtitles and Captions (IMSC) [IMSC11] defined by the Timed Text Working Group (TTWG) ^[7]of the World Wide Web Consortium (W3C), that also published TTML.